KANSAS CITY — With a hard gulp and murmur of “guilty,” Bonnie Sue Lawson, former Buchanan County public administrator, pleaded guilty to federal charges she defrauded 120 disabled clients out of their Social Security payments.

On Wednesday afternoon in Kansas City, Ms. Lawson, 68, waived her right to a grand jury. She pleaded guilty to the charge of defrauding the Social Security Administration, a felony. She faces up to 10 years in prison without parole, plus a fine of up to $250,000.

U.S. District Judge Gary Fenner also may order restitution on about $118,000 she admitted to stealing when Ms. Lawson is sentenced within 90 days. She was released Wednesday on a federal personal recognizance bond.

The 45-minute plea hearing Wednesday effectively ended a protracted investigation by local, state, and federal investigators that began in late 2005 when elderly residents in St. Joseph complained they never received their Social Security payments.

FBI Special Agent Andy Thomure, who is based in St. Joseph and led the federal probe, said despite bringing Ms. Lawson to account, Wednesday was not a “day for a parade” for the citizens of Buchanan County.

“They elected Bonnie Sue three times to a position of trust, and she violated that trust,” said Mr. Thomure, who received the accolades from his FBI colleagues outside the Federal Courthouse.

As to why Ms. Lawson, in office since 1997, was able to bilk client accounts, Mr. Thomure said it was because the job is extremely technical.

“The nature of the job is so complicated. That’s why she got away with it,” he said.

By pleading guilty, Ms. Lawson admitted that between September 2003 and August 2006, she embezzled funds from clients for her own use. Investigators acknowledged Ms. Lawson has a gambling problem.

Since Ms. Lawson’s resignation in August 2006, the Buchanan County public administrator’s office has switched from a fee-based system — in which the administrator reaps fees from handling client accounts — to a salary-based system in which the county receives the fees.

The case was investigated by the FBI, the Social Security Administration’s Office of Inspector General, the St. Joseph Police Department and the Missouri Department of Health and Senior Service.

Federal charges were filed by the office of John F. Wood, U.S. Attorney for the Western District of Missouri.

Ahmad Safi can be reached at ahmadsafi@npgco.com.